Face-down mounted surface acoustic wave device

ABSTRACT

In a chip device in which not only an electrode pattern  25  is provided on a main mounting surface  21   a  of a base  21  but also bump electrodes  22  are provided as external electrodes for face-down mounting, an electrically insulating layer  31  is provided to be put on at least a part of the main mounting surface  21   a  so as to remain edge portions which do not cover at least a part of the electrode pattern  25,  and a protection layer  32  for protecting the main mounting surface is further provided at a distance from the main mounting surface  21   a  so as to be put on the electrically insulating layer  31,  so that the bump electrodes  22  are connected to the electrode pattern  25  while being in contact with the edge portions of the electrically insulating layer  31  and the protection layer  32.

BACKGROUND OF THE INVENTION

The present invention relates to a chip device such as a surfaceacoustic wave device, or the like, face-down mounted on a mount-sidesubstrate (subject mounting substrate) such as a circuit substrate of anelectronic appliance, a package substrate having a wiring circuit formedthereon, or the like, and further relates to a method for producing thechip device.

In recent years, a high-density mounting method has become popular, inwhich bump electrodes (external electrodes) of various chip devices suchas an inductor (L device), a capacitor (C device), a resistor (Rdevice), a surface acoustic wave device, etc. as well as a semiconductordevice, are face-down mounted on a circuit substrate of an electronicappliance. To attain further reduction in size and weight of electronicappliances in future, there are required a chip device having bumpelectrodes capable of being smaller-sized, and a method for producingthe chip device. The background art will be described below with respectto a surface acoustic wave device recently widely used in a mobile radiocommunication appliance, a navigation system, etc., by way of example.

FIG. 6 is a sectional view showing a conventional surface acoustic wavedevice 1 face-down mounted on a circuit substrate 10 as a subjectmounting substrate through bump electrodes 2. An active region 4 havingcomb-like electrodes 3 is formed on a main mounting surface of thesurface acoustic wave device 1. The comb electrodes 3 are connected to aconductor pattern 11 of the circuit substrate 10 through the bumpelectrodes 2 via an electrode pattern which is not shown but formed onthe main mounting surface of the surface acoustic wave device.Incidentally, the electrode bumps 2 are connected to a ground pattern,or the like, of the surface acoustic wave device as well as the combelectrodes. In this manner, the surface acoustic wave device 1 isface-down mounted by means of ultrasonic bonding or by use ofelectrically conductive resin, solder, or the like, so that the activeregion 4 comes face to face with a conductor pattern surface of thecircuit substrate 10.

After face-down mounted on the circuit substrate 10, the aforementionedsurface acoustic wave device 1 as a chip device is generally sealed andprotected with a buffer resin 12 such as silicone resin, or the like,for the double purpose of stress relaxation and electrical insulationand with an exterior resin 13 such as epoxy resin, or the like, for themain purpose of mechanical protection and intensification of moistureresistance.

According to the aforementioned method in which the chip deviceface-down mounted on the circuit substrate is sealed with resin,however, the buffer resin intruded between the chip device and thecircuit substrate is expanded because of temperature change, swelling,etc. to destroy small junctions by means of the bump electrodes tothereby worsen reliability. Particularly, the resin intruded between thesurface acoustic wave device and the circuit substrate is deposited on asurface of the active region to thereby worsen the performance of thesurface acoustic wave device. As shown in FIGS. 7 and 8, therefore, acountermeasure to prevent the influx of the resin is attained so that adam is provided between an upper surface of the circuit substrate andthe main mounting surface of the chip device to form a closed space.FIG. 7 is a plan view showing an example in which not only bumpelectrodes 2 are provided on the main mounting surface of the surfaceacoustic wave device 1 but also a dam frame 8 is provided so as tosurround the active region 4. FIG. 8 is a plan view showing an examplein which discontinuous barriers 9 are formed in some important positionsbetween bump electrodes provided on the main mounting surface of thesurface acoustic wave device 1. Incidentally, an example of theaforementioned structure of the surface acoustic wave device can befound in JP-A-5-55303, etc.

To reduce the size of the chip device more greatly to achievehigh-density mounting such as high-reliable multi-chip on-board, or thelike, however, the following unsolved problems have remained still inthe aforementioned background art.

According to the background art, the dam and the bump electrodes wereformed separately on the chip device. Accordingly, an area for providingthe dam was required on the chip device. Because a width of 1 or severalmillimeters was required to provide the dam frame or the barriers havinga sufficient strength, there was a defect that the resulting shape ofthe chip device became large.

Further, because the dam and the bump electrodes were formed separately,the respective heights of the dam and the bump electrodes on the chipdevice became uneven. There was therefore a problem that no closed spacecould be formed when the chip device was facedown mounted on the circuitsubstrate.

Of course, the discontinuous barriers cannot prevent the influx of theresin perfectly.

Further, it is necessary to reduce the size of the bump electrodes inorder to further reduce the size of the chip device, but the strength ofthe bump electrodes is weakened if the size of the bump electrodes isreduced.

Generally, according to the aforementioned background art, there hasremained a problem that it is impossible to provide any chip device inwhich high-density mounting can be attained by greater reduction in sizeof the chip device.

Incidentally, as a further background art, JP-A-9-246905 has proposed astructure in which not only an enclosure wall is provided so as toenclose the active region of the surface acoustic wave device but alsoan upper space enclosed by the enclosure wall is covered with a coverbody. Also in this case, however, the size of the device is increasedbecause bump electrodes are disposed in the outside of the enclosurewall. Furthermore, because the bump electrodes are in positions far fromthe enclosure wall so as not to be reinforced by the enclosure wall, orthe like, the size of the bump electrodes is required to be increased sothat the bump electrodes have tolerance to stress at the time of bondingand have a necessary fixation strength. Accordingly, it is difficult toadvance the reduction in size of the bump electrodes.

Further, according to the aforementioned background art, it is difficultto make the heights of a plurality of bump electrodes uniform becausethe plurality of bump electrodes are formed on the main mounting surfaceby means of bonding or by use of balls, or the like.

SUMMARY OF THE INVENTION

This invention is designed on the basis of such a knowledge that, whenthe chip device is face-down mounted on the mount-side substrate, it isonly required to provide a gap of several micrometers in the minimumbetween a main mounting surface of a chip device and amount-sidesubstrate such as a circuit substrate, or the like. That is, it is anobject of the present invention to provide a chip device in which boththe reduction in size of external electrodes as bump electrodes and thereduction in external size of the chip device can be attained to therebyachieve high-density mounting to solve the aforementioned problems, anda method for producing the chip device.

In order to achieve the above object according to an aspect of thepresent invention, provided is a chip device in which not only anelectrode pattern is provided on a main mounting surface of a base butalso external electrodes are provided for face-down mounting,characterized in that at least one electrically insulating layer isprovided to be put on at least a part of the main mounting surface so asto remain edge portions which do not cover at least apart of theelectrode pattern, so that the external electrodes are connected to theelectrode pattern while the external electrodes are in contact with theedge portions of the electrically insulating layer.

In the chip device according to the present invention, the edge portionof the electrically insulating layer put on the main mounting surface ofthe chip device so as to have a predetermined thickness serves tosupport the external electrode mechanically. Accordingly, the size ofthe external electrodes can be reduced, for example, to the order ofmicrometers or the order of tens of micrometers as the diameter.Incidentally, the electrically insulating layer may be formed bymaterials other than an inorganic material (SiO2) or an organic materialsuch as polyimide, or the like. Further, the external electrodes are notrequired to be shaped independently, so that the external electrodes maybe formed by a thin-film formation method, a thick-film paste printingmethod, or the like.

In the above chip device, preferably, the electrically insulating layermay include a first electrically insulating layer forming a frame body,and a second electrically insulating layer provided at a distance fromthe main mounting surface so as to be put on the first electricallyinsulating layer to protect the main mounting surface.

In this manner, the main mounting surface is covered with the secondelectrically insulating layer at a gap from the main mounting surface,so that the main mounting surface is protected. Accordingly, not onlythe chip device becomes easy to handle but also the deposition offoreign matters and the contamination with foreign matters can beprevented. Accordingly, the reliability of the chip device can beenhanced.

In the above chip device, preferably, the main mounting surface may havean active region in which comb-like electrodes for a surface acousticwave device are formed as a part of the electrode pattern, and theelectrically insulating layer is interposed between the main mountingsurface and a mount-side substrate while avoiding the active region andcomes into close contact with the mount-side substrate to thereby form aclosed space which encloses the active region.

According to this configuration, the electrically insulating layer whichis formed to a thickness, for example, of from 3 μm to 30 μm whileavoiding the active region serves as a dam to prevent the intrusion ofthe sealing resin into the active region. Accordingly, even in the casewhere resin sealing is performed after a surface acoustic wave device inthe form of a bare chip is face-down mounted on a mount-side substrate,the characteristic of the surface acoustic wave device neverdeteriorates.

According to another aspect of the present invention, provided is amethod for producing a chip device in which external electrodes forface-down mounting are provided on a main mounting surface of a baseafter an electrode pattern is provided on the main mounting surface,characterized by comprising: an electrically insulating layer formationstep of forming at least one electrically insulating layer with apredetermined thickness to be put on at least a part of the mainmounting surface so as to remain edge portions which do not cover atleast a part of the electrode pattern, and an external electrodeformation step of forming external electrodes so that one end of each ofthe external electrodes is connected to the electrode pattern while theexternal electrodes are in contact with the edge portions of theelectrically insulating layer.

In the method for producing a chip device according to the presentinvention, the edge portion formed in the electrically insulating layerformation step and the external electrodes formed in the externalelectrode formation step serve to define the positions and shapes witheach other.

In the above method for producing a chip device, preferably, the methodmay further comprise a face-down mounting step of bonding the externalelectrodes to a mount-side substrate to thereby perform face-downmounting after the external electrode formation step, so that not onlythe external electrodes are connected to a conductor pattern of themount-side substrate but also the electrically insulating layer isbrought into close contact with both the main mounting surface and thesurface of the mount-side substrate in the face-down mounting step.

In this case, the external electrodes come in close contact with theedge portions of the electrically insulating layer when the externalelectrodes are bonded. Accordingly, the external electrodes and the edgeportions of the electrically insulating layer serve to reinforce eachother against deformation of anyone of them, so that the bondingstrength between the external electrodes and the conductor pattern isenhanced. Furthermore, when an adhesive resin is used, the electricallyinsulating layer which is interposed between the chip device and themount-side substrate fulfills contracting force to attract the two toeach other so that the electrically insulating layer serves to enhancemounting strength.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing an embodiment of the presentinvention in the state in which a chip device is face-down mounted ontoa circuit substrate;

FIG. 2 is a sectional view of the chip device in the embodiment of thepresent invention;

FIG. 3 is a plan view of the chip device.

FIGS. 4A to 4D are enlarged sectional views showing the structure of theperiphery of one of bump electrodes provided on the chip device and theprocedure of facedown bonding;

FIGS. 5A to 5F are explanatory views showing the procedure of producingthe chip device;

FIG. 6 is a sectional view showing a background-art chip device;

FIG. 7 is a plan view showing the background art; and

FIG. 8 is a plan view showing another background art example of the chipdevice.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of a chip device and a method for producing the chip deviceaccording to the present invention will be described below withreference to the drawings.

FIG. 1 is a sectional view in the case where a surface acoustic wavedevice as a specific example of the chip device is facedown mounted on acircuit substrate as a mount-side substrate (subject mountingsubstrate). FIG. 2 is a sectional view of the surface acoustic wavedevice. FIG. 3 is a plan view of the surface acoustic wave device.

In these drawings, the surface acoustic wave device 20 has a structurein which an electrode pattern 25 containing comb electrodes 23, a groundpattern not shown, etc. is disposed, by aluminum vapor deposition, orthe like, on a main mounting surface 21 a which is one side surface of apiezoelectric substrate (base of the device) 21 made of lithium niobatecrystal, lithium tantalate crystal, or the like. An active region 24having the comb-like electrodes 23 is formed on the main mountingsurface 21 a. Electrode pattern portions extended from the combelectrodes 23, the ground pattern, etc. form pads 33 as shown in FIG. 3.

An electrically insulating layer 31 (first electrically insulatinglayer) and a protection layer 32 (second electrically insulating layer)are laminated on the main mounting surface of the surface acoustic wavedevice 20 while avoiding the active region 24, so that the layers areprovided as an electrically insulating layer containing an electricallyinsulating resin as a main component. That is, an electricallyinsulating layer 31 having a thickness of about 5 μm and made ofpolyimide resin is provided on the main mounting surface so as to beshaped like a frame to enclose the active region 24. The electricallyinsulating layer 31 which is extended from part of the pads 33 to theoutside of the pads is formed, for example, by patterning of alight-sensitive polyimide resin. A protection layer 32 having athickness of about 20 μm and made of polyimide resin is provided tocover an upper portion of the active region 24 by use of the frame-likeelectrically insulating layer 31 as a spacer, so that a closed space isformed on the active region 24. This protection layer 32 is formed, forexample, by lamination of light-sensitive dry films on the electricallyinsulating layer 31. The protection layer 32 covers the active region 24through the space on the active region 24. Preferably, a cleannon-oxidizing or inert gas is enclosed in the closed space, which coversthe active region 24.

The bump electrodes 22 provided as external electrodes serve as junctionelectrodes. The bump electrodes 22 are disposed in an edge portion (thatis, a frame-like portion which encloses the active region 24) of theelectrically insulating layer composed of the electrically insulatinglayer 31 and the protection layer 32. The bump electrodes 22 areprovided in the inside of holes 34 which are formed to have an innerdiameter of about 10 μm through the edge portion of the electricallyinsulating layer 31 and the protection layer 32. In this case, the bumpelectrodes 22 are made to come in close contact with the electricallyinsulating layer 31 and the protection layer 32 which are formed asinner walls of the holes 34. This bump electrodes 22 are formed from ametal such as copper, nickel, gold, or the like, by a sputtering method,a vapor deposition method, an electrolytic through-hole plating method,or the like. One end of each of the bump electrodes 22 is electricallyconnected to the pad 33 formed on the main mounting surface 20 a of thesurface acoustic wave device 20 and further connected to the comb-likeelectrodes 23, the ground pattern not shown, etc. via the pad 33.

The process of facedown mounting a surface acoustic wave device 20 asthe chip device in FIGS. 1 and 3 on a circuit substrate will bedescribed below with reference to FIGS. 4A to 4D.

As shown in FIG. 4A, the surface acoustic wave device 20 has bumpelectrodes 22 which pierce the edge portion of the electricallyinsulating resin layer composed of the electrically insulating layer 31and the protection layer 32. As shown in FIG. 4B, a conductor pattern 11for mounting the surface acoustic wave device 20 is provided on thecircuit substrate 10. The bump electrodes 22 of the surface acousticwave device 20 are positioned in accordance with the position of theconductor pattern 11. Then, ultrasonic wave and pressing force areapplied to the bump electrodes 22, for example, by an ultrasonic bonder.Thus, as shown in FIG. 4C, the bump electrodes 22, the electricallyinsulating layer 31 and the protection layer 32 are partially deformedso that the conductor pattern 11 of the circuit substrate 10 is broughtinto contact with and bonded to the bump electrodes 22. In thisoccasion, the electrically insulating layer 31 or the protection layer32 is closely bonded to the circuit substrate 10 so that the surfaceacoustic wave device 20 is face-down bonded on the circuit substrate 10.Incidentally, the active region 24 is protected by the protection layer32 through the closed space, so that the active region 24 is notinfluenced by bonding.

Further, when an adhesive agent (new adhesive resin layer) 35 isinterposed between the protection layer 32 and the circuit substrate 10as shown in FIG. 4D, the surface acoustic wave device 20 can bereinforced and fixed on the circuit substrate by use of adhesive forceand contracting force peculiar to high molecules. When the adhesiveagent 35 is used in combination, the protection layer may be omitted.

After the bump electrodes 22 are connected, by means of bonding, to theconductor pattern 11 of the circuit substrate 10 through openingportions from the electrically insulating layer 31 to the protectionlayer 32, as shown in FIG. 1, the upper portion of the surface acousticwave device 20 face-down mounted thus is sealed and protected with abuffer resin 12 and an exterior resin 13 extended onto the circuitsubstrate, if necessary. The buffer resin 12 is constituted by siliconeresin, or the like, for the double purpose of stress relaxation andelectrical insulation. The exterior resin 13 is constituted by epoxyresin, or the like, for the main purpose of mechanical protection andenhancement of moisture resistance.

Referring to FIG. 5, a method for producing the surface acoustic wavedevice 20 as the chip device shown in FIGS. 1 to 4 will be describedbelow. As shown in FIG. 5A, an electrode pattern (pattern for variouselectrodes and wiring) 25 having a thickness of from 500 to 2000angstroms is formed, by aluminum vapor deposition, or the like, on adevice substrate 21 which is a lithium tantalate monocrystallinesubstrate having a thickness of from 0.35 mm to 0.5 mm. Then, as shownin FIG. 5B, light-sensitive polyimide resin having a thickness of 5 μmis patterned and left, so that an electrically insulating layer 31 isformed. As shown in FIG. 5C, a protection layer 32 of polyimide resinhaving a thickness of 25 μm is laminated by use of the electricallyinsulating layer 31 as a spacer, so that a closed space is formed on theactive region. Then, as shown in FIG. 5D, holes 34 each having an upperopening size of 20 μm are provided in the polyimide resin of theprotection layer 32. Further, as shown in FIG. 5E, layers 35 of metalssuch as chrome, copper, nickel, gold, etc. (generally, chrome as thelowermost layer and gold as the uppermost layer) are accumulated by anelectrolytic plating method, a vapor deposition method, or the like, soas to cover the upper surface. Incidentally, because the upper surfaceof the active region 24 on the main mounting surface side is sealed withthe protection layer 32, there is a particular advantage that platingcan be made. Then, as shown in FIG. 5F, the metal layers 35 arepattern-removed by etching, or the like, so that bump electrodes 22 eachhaving an upper outer diameter of about 40 μm are formed.

According to this embodiment of the present invention, the followingeffects can be obtained.

Because the bump electrodes 22 as external electrodes are provided inthe edge portions of the electrically insulating layer (electricallyinsulating resin layer in this embodiment) composed of the electricallyinsulating layer 31 and the protection layer 32, reduction in size ofthe shape of the chip device can be attained compared with thebackground-art chip device having the structure in which the bumpelectrodes are disposed in the outside of the dam frame or barriers.

Because the bump electrodes 22 are formed so as to be in contact withthe edge portions of the electrically insulating layer and reinforced bythe electrically insulating layer, the size of the bump electrodes 22can be reduced. Further, when configuration is made so that theelectrically insulating layer is brought into contact with and bonded tothe circuit substrate at the time of face-down bonding to the circuitsubstrate 10 through the bump electrodes 22, the bonding strengthbetween the bump electrodes 22 and the conductor pattern 11 of thecircuit substrate can be enhanced.

Because not only the active region 24 is enclosed by the frame-likeelectrically insulating layer 31 but also the upper space of the activeregion 24 is closed by the protection layer 32, a closed space sealedagainst the air at a distance of 5 μm is formed on the active region 24.In the background art, when the surface acoustic wave device sealed by aglass casing, a ceramic package, or the like, is not blocked from theexternal environment, slight moisture or foreign matter is deposited onthe surface of the active region to thereby make the characteristic ofthe active region deteriorate. According to the configuration in thisembodiment of the present invention, however, no deterioration ofcharacteristic in handling occurs because the active region 24 iscovered and sealed with the protection layer 32. This effect is notlimited to the embodiment using the surface acoustic wave device as anexample. The same effect as described above is obtained also when thepresent invention is applied to a semiconductor chip.

Because a plurality of bump electrodes 22 are formed simultaneously by athin-film technique and a film-forming technique such as plating, or thelike, the heights of the plurality of bump electrodes 22 can beequalized.

In the aforementioned embodiment of the present invention, a methodusing a light-sensitive dry film has been described as an example of themethod for forming a protection layer. Other than the aforementionedmethod, it is possible to employ any method in which, for example, holesare formed in advance in a bonding sheet using an adhesive polyimidefilm, or the like, before the sheet thus treated is bonded to theelectrically insulating layer.

Alternatively, holes may be formed by use of a laser beam after abonding sheet using an adhesive polyimide film, or the like, in whichthe holes have been not formed yet is bonded to the electricallyinsulating layer.

Further, an anisotropic electrically conductive sheet may be used as theprotection layer. In this case, the protection layer may be formed byattaching the anisotropic electrically conductive sheet to cover theelectrically insulating layer and the bump electrodes after theelectrically insulating layer is formed by patterning and the bumpelectrodes are formed. When the aforementioned chip device is mounted onthe circuit substrate, the whole surface of the anisotropic electricallyconductive sheet can be bonded. Accordingly, sealing characteristic freefrom air leakage is obtained.

Further, the aforementioned embodiment of the present invention has beendescribed about the case where the leading head portion of each of thebump electrodes forms a flat surface. However, for example, the centerportion of the leading head portion of each of the bump electrodes maybe shaped to be hollow. Further, the aforementioned embodiment has beendescribed about the case where the head portion of each of the bumpelectrodes is wider than its base portion. However, for example, each ofthe bump electrodes may be shaped so as to have an equal width from thebase portion to the leading head portion.

When the configuration shown in the aforementioned embodiment of thepresent invention is used, the main mounting surface of the chip deviceis covered with the protection layer. Accordingly, various differentbump materials such as solder, gold, electrically conductive resin, etc.can be used for the bump electrodes of the chip device. Furthermore,various connection means such as cream solder, electrically conductiveresin, ultrasonic gold bonding, etc. can be used. As a result, whenvarious kinds of chip devices are to be mounted onto one and the samecircuit substrate, the various kinds of chip devices can be mounted ontothe one and the same circuit substrate simultaneously by various bondingmethod so that, for example, one chip device is mounted by soldering andanother chip device is mounted by use of an electrically conductiveadhesive agent. Furthermore, the atmosphere and temperature, the reflowcondition, the ultrasonic bonding condition, etc. at the time of bondingcan be selected widely. That is, according to the present invention,there is produced an excellent effect that a plurality of different chipdevices are MCM-mounted (MCM: multi-chip module) onto one and the samecircuit substrate freely and easily.

Incidentally, after the chip device according to the embodiment of thepresent invention is MCM-mounted onto the circuit substrate, the wholeof the chip device can be also covered with the exterior resin.Accordingly, various changes can be made so that, for example, theprotection layer is omitted or simplified and the outside of the chipdevice is finally sealed with resin.

Although the embodiment of the present invention has been describedabove, it will be self-evident to those skilled in the art that thepresent invention is not limited thereto but various modifications andchanges may be made within the scope of claims.

As described above, according to the present invention, externalelectrodes are provided so as to come in close contact with the edgeportions of the electrically insulating layer provided on the mainmounting surface of the chip device to be face-down mounted onto themount-side substrate. Accordingly, the size of the chip device can bereduced. Furthermore, there can be provided the chip device which hashigh reliability and in which high-density mounting can be made.Further, a surface acoustic wave device excellent in reliability andsmall in size can be provided by application of the present invention tothe surface acoustic wave device.

Further, in the producing method according to the present invention,there are provided the electrically insulating layer formation step andthe external electrode formation step of producing external electrodesso that the external electrodes come in contact with the electricallyinsulating layer. Accordingly, there is an effect that the chip devicehaving small external electrodes can be formed.

What is claimed is:
 1. A chip device comprising: a device substrate; anelectrode pattern and an active region provided on a main mountingsurface of said device substrate; an external electrode provided forface-down mounting; and a first electrically insulating layer formed onat least a part of said main mounting surface to form a frame body toexpose said active region and at least a part of said electrode pattern;wherein said external electrodes are connected to said electrode patternwhile said external electrodes are in contact with edge portions of saidelectrically insulating layer; and said first electrically insulatinglayer is interposed between said main mounting surface and a mount-sidebase substrate while not extending completely under said active region.2. A chip device according to claim 1, further comprising: a secondelectrically insulating layer provided at a distance from said mainmounting surface so as to be put on said first electrically insulatinglayer to protect said main mounting surface.
 3. A chip device accordingto claim 1, wherein said main mounting surface in said active region hascomb electrodes for a surface acoustic wave device formed as a part ofsaid electrode pattern, and said first electrically insulating layercomes into close contact with said mount-side substrate to thereby forma closed space which encloses said active region.
 4. A chip deviceaccording to claim 2, wherein said main mounting surface in said activeregion has comb electrodes for a surface acoustic wave device formed asa part of said electrode pattern, and said first electrically insulatinglayer comes into close contact with said mount-side substrate to therebyform a closed space which encloses said active region.